The present invention relates to a feed and control system for an internal combustion engine fed with two different fuels.
Internal combustion engines able to operate by burning a first fuel (petrol) or alternatively a second fuel (liquid gas or LPG or methane) have been known for some time. Such engines are used in so-called two-fuel vehicles.
These fuels are suitably fed to the engine via corresponding feed systems each currently comprising their own engine feed and operation devices. The fuels are fed into the engine explosion chambers by introduction members or injectors associated with each feed system and totally separate from each other. The engine hence comprises introduction members or injectors for the petrol and separate injectors for the gas.
Existing gas injection systems with multiple injectors (or multipoint injection systems) for two-fuel vehicles are known to be based on an engine control unit which controls the injection times for the petrol injectors (petrol ECU or electronic control unit) and a gas control unit which controls the injection times for the gas injectors (gas ECU). This can either operate independently of the petrol control unit (in which case the system is a replication or duplication of the petrol system) or can reprocess the output injection times from the petrol control unit (in which case it is known as a corrector or slave system for the signals generated by this latter). In the first case the control unit for the gas system constitutes an actual engine control system which is independent of the petrol system and requires various input signals originating from the engine (lambda probe, air temperature, water temperature, engine r.p.m., manifold pressure, etc.), whereas in the second case it is not independent, it generally having less inputs and its main task being to reprocess the first fuel injection times acquired for controlling the petrol injectors. In gas operation, the petrol system control signals are redirected to “emulation” loads (reactances which simulate the reactances of the petrol injectors) so that the petrol ECU continues to operate (executing its usual functions such as ignition management, idling control, diagnosis, etc) as if the engine were still fed with petrol. However, in traditional systems the gas injection times, under the same engine conditions, are generally different from those implemented by the petrol ECU, with consequent possible incorrect operation of the engine when fed with gas. The traditional systems are fairly complex and costly. Moreover, even in the most simple (and often efficient) corrector systems, the reprocessing of the injection times introduces delays and disturbances into the control chain of the original system, the performance of which is therefore modified in a pejorative sense.
In addition, with said known injection systems, there is a duplication of cabling within the engine, making the feed system for the second fuel costly both because of the use of such cabling and because of the time for its installation.
Internal combustion engines are also known in which a single control unit is provided for both the petrol injectors and the gas injectors.
DE19704640 relates to an engine comprising a plurality of nozzles arranged to feed two different types of fuel into the explosion chamber, a first fuel being used to “ignite” the second fuel. That text states that the engine can also operate just with the fuel used to ignite the second fuel.
In that text there is no clear description relative to a single control unit for feeding the different fuels through the various nozzles nor is there a clear description of any method for controlling the fuel emission nor, in particular, is operation with two alternative fuels described. In effect, according to that text, in a first method of engine operation the fuels are injected jointly into the engine whereas in a different method of engine operation only one of these fuels is used for said operation. Nothing is stated regarding the times for injecting the different fuels into the cylinder.
U.S. Pat. No. 6,035,837 describes a system or engine fed with two fuels. The engine comprises however a single series of injectors to which the two fuels are fed alternatively. It describes the use of a single control unit (ECU) which controls the opening of a valve receiving said two fuels, such that it feeds them to the engine alternatively. It also describes the control of any fuel mixture fed to the engine by measuring the conductivity and/or temperature and/or pressure within the conduit common to the injectors.
The US patent text does not provide for direct injector control; even in this case nothing is stated regarding the possibility of controlling parameters such as pressure and temperature of the second fuel such that the injection times for the two fuels are equal.
EP0922843 aims to solve the problem of maintaining the petrol operation system efficient even when the engine is fed with gas (liquid or methane). For this reason, the patent text under examination provides for electronic control means which oblige the engine to be restarted, after a stoppage during which the gas tank is filled, in the petrol operation mode only if a level increase in the gas tank is sensed. The text describes the presence of a single engine control unit both during gas operation and during petrol operation, said operation being conventional.
Nothing is stated in the text regarding the times for injecting said fuels into the cylinder.
Finally, EP0872634 relates to a control device for an engine fed with two fuels comprising, however, two separate units for controlling corresponding injectors during engine operation with different fuels. The unit controlling the gaseous fuel injectors operates in accordance with data present in the unit controlling the liquid fuel injectors. These data are modified by the gaseous fuel control unit to obtain operative signals for the injectors of this gaseous fuel.